/**
 * Created with IntelliJ IDEA
 * Description
 * User: 王杰
 * Date: 2025-06-01
 * Time: 11:46
 */
public class MyQueue {
    static class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }

    public ListNode first = null;
    public ListNode last = null;

    public int usedSize = 0;

    // 尾插
    public void offer(int val) {
        ListNode cur = new ListNode(val);
        if (first == null) {
            first = last = cur;
        }else {
            last.next = cur;
            cur.prev = last;
            last = last.next;
        }
        usedSize++;
    }

    // 头删
    public int poll() {
        if (isEmpty()) {
            return -1;
        }else {
            int val = first.val;
            first = first.next;
            if (first != null) {
                first.prev = null;
            }
            usedSize--;
            return val;
        }
    }


    public int peek() {
        if (isEmpty()) {
            return -1;
        }else {
            return first.val;
        }
    }

    public boolean isEmpty() {
        return usedSize == 0;
    }
}
